The Apple (AAPL -1.22%) rumor mill was a mixed bag in 2014. A few announcements, including Apple Pay and Apple Watch, were widely discussed months, and even years, ahead of their unveiling. Others, like a sapphire screen-equipped iPhone, and a full-featured Apple TV, remained elusive.

Will the same hold true for 2015? Heading into the new year, expectations are high for the Cupertino tech giant. Although investors shouldn't assume these products are guaranteed (far from it), a few could arrive in Apple stores next year.

The iPhone 6S: A smaller screen, a better camera, and a 3D display?
Unless Apple decides to alter its nomenclature, an iPhone 6S is practically guaranteed. But what will that device entail? Past iPhone "S" generations introduced radical new features -- a video camera, Siri, TouchID -- the same could hold true for the iPhone 6S.

Daring Fireball's John Gruber claims the iPhone 6S could include a radically improved camera, one on par with modern DSLRs. China's Economic Daily News (via BGR) has said the iPhone 6S will feature a 3D display -- a report backed up by a recently granted patent. Neither would be particularly shocking.

There's also some speculation on the screen size: A report from China's Feng (via GSM Arena) claims that Apple will bring back the 4-inch display. Three different sized iPhones (iPhone 6S, iPhone 6S Plus, and iPhone 6S Minus, perhaps?) could appeal to a diverse customer base, ensuring that there's a high-end iPhone with a screen size to suit every taste.

The answer to the iPad's problem?
Demand for the iPhone 6 has been outstanding; so strong, in fact, that Apple has struggled to keep up, and admitted to selling everything it can make. Clearly, the move to a larger screen proved to be a powerful catalyst, enticing existing iPhone owners to upgrade, and perhaps winning over some Android converts.

Could something similar work for the iPad? Rumors of a larger iPad -- a so-called iPad Pro -- have been around for over a year. Apple's competitors in the tablet space, including both Samsung and Microsoft, have embraced the concept, releasing tablets with screens larger than 12-inches.

The iPad's struggles have been one of the few problems Apple has faced in 2014 -- demand for Apple's tablets has contracted. A larger (and presumably more expensive) iPad might not rejuvenate iPad sales overnight, but it could appeal to business users seeking a hybrid-like device.

A revolutionary new Macbook?
Apple will, almost assuredly, update its Mac models in 2015 -- improved processors and more memory seem like a safe bet -- but it could have something in store that's a bit more significant.

In Oct. 2013, KGI Securities' Ming-Chi Kuo claimed that Apple was hard at work on a 12-inch version of the Macbook Air, one that would offer unparalleled portability and -- like the original Macbook Air -- redefine laptop computing. Since then, several other sources have made similar reports, though this new Macbook has yet to be unveiled.

Currently, Apple offers two versions of the Macbook Air: one with an 11-inch screen, another with a 13-inch. Offering as few models as possible is a long-standing Apple tradition; if it believes it can deliver a hybrid that offers the best of both worlds (portability and productivity), replacing the current Macbook Air models with a single, 12-inch Mac wouldn't be surprising.

Is 2015 finally the year for the Apple TV?
Apple will release at least one new major product in 2015: the Apple Watch will go on sale at some point during the first half of the year. Could Apple shock investors with a second?

A full featured, integrated Apple television has been widely rumored for half a decade at this point. Sell-side analysts have, year after year, promised that the Apple TV was right around the corner, only to be proven wrong. Still, the Apple TV seems likely to appear at some point -- Tim Cook has, on several occasions, hinted at an interest in the living room.

Even if Apple doesn't release a full-on TV, an update to its Apple TV set-top box seems warranted. The device has seen relatively few changes since the third generation was released in early 2012, and though it has been updated with more apps, it now lags its competitors in terms of processing power, features, and market share. A fourth generation Apple TV could add support for emerging technologies like 4K streaming, and perhaps offer the ability to play iOS games on the big screen.